The only 538 I have ever seen was due to user error. I have pulled codes on the EEC system many times and still get a occasional 538 error. If you don't goose it at just the exact time it will pop up.I normally disregard that error if I see it.
If it's the same concept of FPR that's used on the OHV 4.0, namely it uses engine vacuum, then the test is very simple. Shut off the engine after it's ran long enough that it's known that the flood problem will occur, pull the rubber vacuum hose from and at the FPR and look/smell inside. Any gas in there and the FPR has a failed diaphragm and the unit needs repolacing.
Charlie wins a all expense pay vacation to were ever he is right now.
Put new temp senders in the thing idle evened out, temp gauge runs in them middle. regulator reduced the hot starting problem to a light stumble for first second. A4le got a service and poor boy flush (hate working on car automatics).
now to find or repair the cracked flanges on the muffle i found.
bring the grand to less the $1500 total in this car over 4 years. including buying it :